Apile of crumpled cars is ready for 10a<1inginto a giant

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1 INTEGRATING CHEMISTRY,,~ ~c..tloa... Cycles of Matter DISCOVER Are You Par' 01 a Cyde? 1. mhold a small mirror a few IL:J centimeters from your mouth. 2. Exhale onto the mirror. 3. Observe the surface of the mirror. Think It Over Inferring What is the substance that forms on the mirror? Where did this substance come from? Apile of crumpled cars is ready for 10a<1inginto a giant compactor. Junkyard workers have already removed many of the cars' parts. The aluminum and copper pieces were removed so that they could be recycled, or used again. Now a recycling plant will reclaim the steel in the bodies of the cars. Earth has a limited supply of aluminum, copper, and the iron needed to make steel. Recycling old cars is one way to provide a new supply of these materials. Recycling Matter The way matter is recycled in ecosystems is similar to the way the metal in old cars is recycled. Like the supply of metal for building cars, the supply of matter in an ecosystem is limited. If matter could not be recycled, ecosystems would quickly run out of the raw materials necessary for life. Energy, on the other hand, is not recycled.you must constantly supply a car with energy in the form of gasoline. Ecosystems must also be constantly supplied with ~nergy,usually in the form of sunlight. Gasoline and the sun's energy cannot be recycled-they must be constantly supplied. As you read in Section 1, energy enters an ecosystem and moves from the producers to the consumers to the decomposers. In contrast, matter cycles through an ecosystem over and over. Matter in an ecosystem includes water, oxygen, carbon, nitrogen, and many other substances. To understand how these substances cycle through an ecosystem, you need to know a few basic terms that describe the structure of matter. Matter is made WJ'lat three major processes make up the water cycle? How is carbon dioxide used by producers? Reading Tip As you read, use the section headings to make an outline of the section. Cars awaiting recycling at a Utah plant T

2 Figure 8 In the water cycle, water moves continuously from Earth's surface to the atmosphere and back. Interpreting Diagrams In which step of the water cycle does water return to Earth's surface? up of tiny particles called atoms. Combinations of two or more atoms chemically bonded together are called molecules. For example, a molecule of w~ter consists of two hydrogen atoms bonded to one oxygen atom. In this section, you will learn about some of the most important cycles of matter: the water cycle,the carbon and oxygen cycles, and the nitrogen cycle. harpen your Developing Hypotheses You're having.-"-"'~''--", cocoa at aa.~" friend's house. on a cold, rainy day. As your friend boils some water, you notice that a window next to the stove is covered with water droplets. Your friend thinks the window is leaking. Using what you know about the water cycle, can you propose another explanation for the water droplets on the window? 52. E The Water Cycle How could you determine whether life has ever existed on another planet in the solar system? One piece of evidence scientists look for is the presence of water. This is because water is the most common compound in all living cells on Earth. Water is necessary for life as we know" it.. Water is recycled through the water cycle. The water cycle is the continuous process by which water moves from Earth's surface to the atmosphere and back. The processes of evaporation, condensation, and precipitation make up the water cycle. As you read about these processes, follow the cycle in Figure 8. Evaporation The process by which molecules of liquid water absorb energy and change to the gas state is called evaporation. In the water cycle liquid water evaporates from Earth's surface and forms water vapor, a gas, in the atmosphere. Most water evaporates from the surfaces of oceans and lakes. The energy for evaporation comes from the sun.

3 ~ Some water is also given off by living things. For example, plants take in water through their roots and release water vapor from their leaves.youtake in water when you drink and eat. Yourelease liquid water in your wastes and water vapor when you exhale. Condensation What happens next to the water vapor in the ( atmosphere? As the water vapor rises higher in the atmosphere, it cools down. When it cools to a certain temperature the vapor turns back into tiny drops of liquid water. The process by which a gas changes to a liquid is called condensation. The water droplets collect around particles of dust in the air, eventually forming clouds like those in Figure 8. Precipitation As more water vapor condenses, the drops of water in the cloud grow larger and heavier. El,rentuallythe heavy drops fall back to Earth as a form of precipitation-rain, snow, sleet, or hail. Most precipitation falls back into oceans or lakes'. The precipitation that falls on land may soak into the soil and become groundwater. Or the precipitation may run off the land, ultimately flowing into a river or ocean once again. M'~ What change of state occurs when water from the surface of the ocean enters the atmosphere as water vapor? The Carbon and Oxygen Cycles Two other chemicals necessary for life are carbon and oxygen. The processes by which they are recycled are linked together, as shown in Figure 9. Carbon is the building block for the matter that makes up the bodies of living things. It is present in the atmosphere in the gas carbon dioxide. ~~ers take in carbon dioxide from Figure 9 This scene shows how the carbon and oxygen cycles are linked together. Producers use carbon dioxide to carry out photosynthesis. In this process, carbon is used to create sugar molecules such as those found in apples. The producers release oxygen, which is then used by other organisms. These organisms take in carbon in food and release it in the form of carbon dioxide again.

4 Figure 10 In the nitrogen cycle, nitrogen moves from the air to the soil, into living things, and back into the air. Interpreting Diagrams How do consumers obtain nitrogen? ~ Free nitrogen in air the atmosphere during photosynthesis. In this process, the producers use carbon from the carbon dioxide to produce other carbon-containing molecules. These molecules include sugars and starches. To obtain energy from these molecules, consumers break them down into simpler molecules. Consumers release.r water and carbon dioxide as waste products. At the same time, oxygen is also cycling through the ecosystem. Producers release oxygen as a result of photosynthesis. Other organisms take in oxygen from the atmosphere and use it in their life processes. wf e~ How is oxygen returned to the environment? The Nitrogen Cycle Like carbon, nitrogen is a necessary building block in the matter that makes up living things. Since the air around you is about 78 percent nitrogen gas, you might think that it would be easy for living things to obtain nitrogen. However, most organisms cannot use the nitrogen gas in the air. Nitrogen gas is called "free" nitrogen, meaning it is not combined with other kinds of atoms. Most organisms can use nitrogen only once it has been "fixed," or combined with other elements to form nitrogen -containing compounds. You can follow this process in Figure 10 below. 1 Bacteria relecf",se some free nitrogen back to air Decomposers break down wastes and the re[l1ains of organisms and return nitrogen compounds to soil Bacteria in root nodules fix free nitrogen into compounds 54 +E

5 Nitrogen Fixation The process of changing free nitrogen gas into a usable form of nitrogen is called nitrogen fixation. Most nitrogen fixation is performed by certain kinds of bacteria. Some of these bacteria live in bumps called ~ (NAHJ oolz) on the roots of certain plants. These plants, known as legumes, include clover, beans, peas, alfalfa, and peanuts. The relationship between the bacteria and the legumes is an example of mutualism. As you recall from Chapter 1, a symbiotic relationship in which both species benefit is called mutualism. Both the bacteria and the plant benefit from this relationship: The bacteria feed on the plant's sugars, and the plant is supplied with nitrogen in a usable form...jt!.!.f&f!la.fh\j.~ Many farfil.elfs make use of the nitrogen- =..J TECHNOLOGY fixing bacteria in legumes to enrich their fields. Every few years, a farmer may plant a legume such as alfalfa in a field. The bacteria in the alfalfa.roots build up a new supply of nitrogen compounds in the soil. The following year, the new crops planted in the field benefit from the improved soil. (~, \/1 Figure 11 Lump noqul~jj,are Return of Nitrogen to the Environment Once the nitrogen has been fixed into chemical compounds, it can be used by clover plant. Bacteria inside the clearly visible on t~f this organisms to build proteins and other complex substances. nodules carry out nitrogen fixation. } Decomposers break down these complex compounds in animal wastes and in the bodies of dead organisms. This returns simple ') nitrogen compounds to the soil. Nitrogen can cycle from the soil to producers and consumers many times. At som~ point, however, bacteria break down the nitrogen compounds completely. These bacteria release free nitrogen back into the air. Then the cycle starts again. '~"~'''''''''''''''~''5!!S''"''''''''C''''''''''~'''''.'N~'' \,Section 2 Review 'C' "',"'''' --" '.,' Name and define the three major processes that occur during the water cycle. 2. Explain the role of plants in the carbon cycle. 3. How is nitrogen fixation a necessary part of the nitrogen cycle? 4. Where do nitrogen-fixing bacteria live? 5. Thinking Critically Comparing and Contrasting Explain how the movement of matter through an ecosystem is different than the movement of energy through an ecosystem.... f Chefk Your Progress : Once your teacher has f approved your plan, place the : waste into your compost chambers. : Record your hypothesis about the effect : of the variable you are investigating. : Observe the two containers daily. (Hint: If : there are no signs of decomposition after : several days, you may wish to stir the f contents of each chamber. Stirring allows : more oxygen to enter the mixture.) Chapter 2 E + 55